Many pyrrole heptanoic acid derivatives have been synthesized. Of these, [R—(R*,R*)]-2-(4-fluorophenyl)-β,δ-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino)carbonyl]-1H-pyrrole-1-heptanoic acid is a statin drug whose mechanism of action has been elucidated in detail and is known to be the most therapeutically effective drug available for reducing the concentration of low-density lipoprotein (LDL) as a risk factor of thrombosis. The pyrrole heptanoic acid derivative is currently commercially available in the form of hemicalcium salt trihydrate. The pyrrole heptanoic acid hemicalcium salt is represented by Formula 1:

[R—(R*,R*)]-2-(4-fluorophenyl)-β,δ-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenyl-amino)carbonyl]-1H-pyrrole-1-heptanoic acid was first disclosed in U.S. Pat. No. 4,681,893. U.S. Pat. No. 5,273,995 teaches that the compound of Formula 1 is prepared by crystallization from a brine solution resulting from the transposition of the sodium salt with CaCl2 and further purified by recrystallization from a 5:3 mixture of ethyl acetate and hexane.
Various processes and key intermediates for preparing amorphous forms of the compound' of Formula 1 are found in the literature, for example, U.S. Pat. Nos. 5,003,080, 5,097,045, 5,103,024, 5,124,482, 5,149,837, 5,155,251, 5,216,174, 5,245,047, 5,248,793, 5,280,126, 5,397,792, 5,342,952, 5,298,627, 5,446,054, 5,470,981, 5,489,690, 5,489,691, 5,510,488, 5,998,633 and 6,087,511. However, the amorphous forms have unsuitable filtration and drying characteristics for large-scale production and must be protected from heat, light, oxygen and moisture.
On the other hand, polymorphs are considered as distinct solids because they have different physical properties despite the same molecular formula. Crystalline forms of the compound of Formula 1 are the subjects of U.S. Pat. Nos. 5,969,156 and 6,121,461. Further, PCT International Publication No. WO 01/36384 discloses a polymorphic form of the compound of Formula 1. There is a need in the art for crystalline forms of the compound of Formula 1 that are more stable and easier to handle than the known crystalline forms.